If you want to become a betting expert, you need to know where the odds that determine your sports picks come from.
Their origin involves several expert analyses that we will explain to you here in a simple way.
How are they established?
Bookmakers take various factors into account. The streak of a team, the level of its players, where the match will be played and even the weather are some of the many things to take into account when determining the odds.
To do this, they use algorithms and mathematical programmes to help calculate odds according to the match and the teams involved, but they also take into account how punters tend to react.
Who defines them?

Odds don’t just magically appear. Each bookmaker is in charge of defining their odds, although they usually do so based on the figures that Las Vegas casinos come up with before and during each event.
Can they change?
Yes! Odds are not final and are constantly changing. The first number that appears is known as the ‘starting line’ and can change from there.
Its variation depends on how bettors react; if they start betting a lot on a line, the odds will start to decrease (i.e. turn or become more negative).
In some cases the line refers to the number of points in a match. For example, if in a game between the San Francisco 49ers and Green Bay Packers the starting line is 50 points, bettors will make their decisions based on which outcome they think is more likely; in those cases the line could go up or down depending on how the bets are moving.
How do odds work for your bets?
If you’re just starting to bet and have questions about the odds that accompany the matches, we’ve got you covered with this guide.
To become an expert bettor you need to start with the basics. The first thing you need to understand is how the odds work, those numbers that appear bets.
To clear your doubts, we bring you a simple explanation about them, so you understand what they are and how they can help you make better betting decisions.
What are they for?
Odds ratios serve a purpose: to define the probability of an outcome occurring in an event and to establish the odds you would win if you guess correctly.
For example, odds can indicate how likely it is that a team will win, draw or lose or that a specific event will occur during the match (total goals, points or touchdowns).
How do they read?

Let’s go with a practical case for you to understand better. Let’s say Real Madrid (-120) and Barcelona (+130) are playing. When a team is favourite to win, its odds will have a negative number (Real Madrid), while the underdog will have a positive number (Barcelona). In football you will also see the option of a draw, which in most cases will be a positive odds.
You might also find some sporting events where both teams have positive odds or negative odds; in these cases, the favourite team is the one with the more negative number (although it sounds strange).
What types are there?
You have three odds options: American (e.g. -130), decimal (1.50) and fractional (117/100), being the American odds the most used in the betting world and the one we will use to explain how they work.
If you want to change to another format it is easy: in the sports section you can find a tab above the featured events where you can choose the one you like the most.
How do I calculate my winnings?
There are formulas depending on the odds to calculate your winnings, but we don’t want to bore you or make you get out your calculator.